Constructivism refers to a theory or set of theories about learning that emerged in Europe and were introduced to the United States in the 1970s, during a period of social reform and civil rights movements and challenges to the "old" order and its hierarchies. Constructivism refers both to a learning theory and to an epistemology of learning. Constructivist theory posits that people construct their own understanding and knowledge of the world through experiencing the world, and reflecting on those experiences. Jean Piaget, a Swiss-born professor of psychology and student of biology, devoted his life to the question of cognitive development, and particularly to classifying the stages of human development. Piaget was not only a psychologist but also a biologist. He strongly defended and promoted the scientific method, and he believed that the scientific approach was the only valid way of gaining access to knowledge.